1. Field of the Invention
The present invention generally relates to halftoning techniques in printers and displays and, more particularly, to a method and apparatus for halftoning with a display or printing medium such that the displayed (or printed) image pixels have different characteristics depending on conditions of the viewing environment such as viewing angle, temperature and lighting conditions.
The inventive halftoning method and apparatus generate a halftoned output such that a different image is displayed under each condition of the viewing environment.
2. Description of the Related Art
Most printers and displays show images which look relatively the same under different viewing conditions. However, this is not true for all printing technologies and displays. For instance, for a type of LCD (Liquid Crystal Display) display commonly used in laptop computers, the image pixels change color and brightness drastically as the viewing angle is changed. Other examples include inks which change color or density, as the temperature is changed, or inks which change color or density when the printed paper is illuminated with ultraviolet light.
Given images N1, N2 , . . . a problem arises of how to generate an image such that it looks like N1 under viewing condition 1, it looks like N2 under viewing condition 2, etc.
Further, because images printed by a printer or displayed on a display can change color characteristics as the conditions of the viewing environment change, another problem arises as to how to generate images which look the same even as these viewing conditions change.
Other systems exist which display two or more images depending on viewing angles, such as those used on decals, baseball cards, etc. There are several differences between these systems and the present invention. First, these printed papers in the conventional systems are designed to display different images at different angles, and thus no special processing of the image is needed. In the present invention, the display (or printing medium) is not specifically designed to display different images at different viewing conditions, and therefore the present invention teaches methods to process the images so that the display will show different images under different viewing conditions.
Second, the conventional systems mainly deal with different viewing angles, whereas the present invention can also be applied to showing different images under different lighting conditions, temperature, etc.
Third, the conventional systems are mainly applicable to printed images, whereas the present invention is also applicable to displays which can accommodate video.